Winter is back in town

It's a first day of climatological winter, and the coldest 1st of December in Berlin since inception of instrumental measurements. Cold winter is coming indeed, but it does not mean that anthropogenic impact on environment is negligible.

The daily North Atlantic Oscillation (NAO) index, as obtained from the Climate Prediction Center (CPC). Check their web pages for the most recent figure and the methodology.

Internal climate variability - phenomenons such as El Nino, Northern Atlantic Oscillation (NAO), Atlantic Meridional Overturning Circulation (AMOC), are in their phases that favor cold winter. For example NAO negative phase results with increased snowfall above the Scandinavia and Western Europe.
We saw a consistently negative NAO since mid-August (see figure), strong at times, and interupted with positive phase in October (remember "Goldene Oktober" in Germany). Since mid-November we see very strong negative phase (remember I told you Mr. November did not let us down). Forecasters are expecting generally negative NAO to continue through December and probably until mid January with an occasional period of +NAO possible. More frequent exchange of positive and negative phases is expected during second part of January and February. Furthermore some researchers suggest that heat transport between tropical and polar latitudes is reduced due do weakening of Atlantic Meridional Overturning Circulation (AMOC) i.e. Gulf stream does not produce that much heating as it used to due to Greenland ice-sheet melting and decreased ocean thermohaline mixing.